It is known to use digital watermarks, and to obtain such marks by embedding a digital string into an image. The digital watermarks can be created either in a spatial domain or in a transform domain. In transform domain digital watermarking, the digital string is embedded using a transformation space, such as Fourier transform or the like, to obtain a spread spectrum characteristic of noise insensitivity. Correspondingly, the digital watermark is not an image and can not be simply reconstructed or verified optically, though the actually encoded digital watermark data can be arbitrary, thus also an image in some other transform domain. An example of spatial domain digital watermarking is found in U.S. Pat. No. 6,252,971 to S. Wang, for “DIGITAL WATERMARKING USING PHASE-SHIFTED STOCLUSTIC SCREENS,” issued Jun. 26, 2001, where the watermark can be reconstructed as image directly in the space domain.
Classical watermarks are image-wise watermarks, meaning that they can be viewed by a user, normally to verify authenticity, but often only to establish a perception of value or beauty. Image-wise digital watermarks exist in the form of glossmarks, correlation marks and embedded image watermarks as described, for example in U.S. patent application Ser. No. 11/034,131 (above), as well as U.S. patent application Ser. No. 10/876,001 (U.S. Publ. 20050128524 A1), for “ENHANCEMENT OF GLOSSMARK IMAGES AT LOW AND HIGH DENSITIES,” by Liu et al., filed Jun. 24, 2004, also incorporated herein by reference in its entirety.
The advantage of such watermarks is that they more closely resemble classical watermarks, albeit with the added capability of variable content. This variable content, however, also directly interacts with the background image and a truly automated use of variable watermarks requires the correct positioning (or identification of the watermark location) based on the watermark content and the image content. In other words, when an image-wise watermark is to be employed, and it is desirable to either make the mark visible or to hide the mark, the “best” or preferred position at which such a mark should be reproduced in the image is strongly dependent upon the nature of the mark as well as the image—where simply repositioning the mark within an image may significantly alter the detectability (desired/undesired) of a mark.
U.S. Pat. No. 6,956,958, by Z. Fan et al. “METHOD OF EMBEDDING COLOR INFORMATION IN PRINTED DOCUMENTS USING WATERMARKING”, issued Oct. 18, 2005, describes a method of enhancing color fidelity in multi-reproduction that includes an encoding part, which usually resides in a printer (or the printing part of a copier, but may also be resident in software stored in a computer) and a decoding part which usually resides in a scanner (or the scanning part of a copier, but may also be resident in software stored in a computer) so as to add color fidelity information directly to the output print. Each part can be divided into layers where the top layers are responsible for management of color information while the bottom layers are responsible for embedding/detection of digital watermarks containing the color information.
Accordingly, the present disclosure is directed to a system and a method for determining preferred image locations for placing watermark information for both hidden and obvious marks. Preferred locations provide either a high degree of hiding or visibility depending on the goal. At least three metrics may be employed in making a determination of a preferred position of a watermark, including (i) image value, (ii) image/watermark value similarity, and (iii) image/watermark contrast similarity.
Disclosed in embodiments herein is a method for determining a location for an image-wise watermark in relation to a target image, comprising: analyzing the target image by dividing the target image into a plurality of smaller areas and determining a characteristic metric for the areas thereof; and determining, based upon the characteristic metric, at least one location for the watermark image to be overlaid onto the target image.
Also disclosed in embodiments herein is a print production system for determining a location for an image-wise watermark in relation to a target image, comprising: a processor for analyzing the target image by dividing the target image into a plurality of smaller areas and determining a characteristic metric for the areas thereof; memory for recording the characteristic metric data for each of the areas analyzed by the processor; said processor further determining, based upon the characteristic metric, at least one location for a watermark image to be overlaid onto the target image, and overlaying said watermark image on the target image in the at least one location; and a printing engine for receiving the target image with the overlaid watermark image and rendering the image on a substrate.
Further disclosed in embodiments herein is a method for printing variable data with a watermark, comprising: receiving a target image into which an image-wise watermark is to be embedded; receiving a watermark image; analyzing the target image by dividing the target image into a plurality of smaller areas and determining a characteristic metric for the areas thereof; analyzing the watermark image by dividing the watermark image into a plurality of smaller areas and determining a characteristic metric for the areas thereof; and determining, based upon at least one of the characteristic metrics, at least one location for the watermark image to be overlaid onto the target image.